The production of arylphosphines can be complicated if the substituents on the phosphorus are not identical. In situations where production of mixed alkyl-aryl phosphines is desired, the synthesis generally involves the use of at least one type of organo alkali metal intermediate, the synthesis of which is often difficult or inefficient.
One class of bidentate phosphorus ligands which are mixed alkyl-aryl phosphines has become of interest as precursor of a catalyst composition useful in the production of a type of polymeric material known as polyketones. These polyketones are linear alternating copolymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon. Polymerization takes place in the presence of a catalyst composition formed from a compound of palladium, cobalt or nickel, an anion of certain strong non-hydrohalogenic acids and the bidentate ligand. Such bidentate phosphorus ligands are illustrated by the formula ##STR1## wherein R.sup.1 independently is an aryl substituent and R is a divalent bridging group, often trimethylene. The processes for production of the polyketones are illustrated by published European Patent Applications 0,121,965 and 0,181,014. Good results are obtained employing ligands in which each R.sup.1 is phenyl, an illustrative ligand therefore being 1,3-bis(diphenylphosphino)propane. One of the least complicated methods of producing this ligand involves the reaction of an alkali metal di(R.sup.1)phosphide, e.g., sodium diphenylphosphide, with an .alpha.,.OMEGA.-dihaloalkane such as 1,3-dichloropropane. Corresponding methods produce other bis(diarylphosphino)alkanes.
Recent process developments in polyketone production have shown that particularly good results are on occasion obtained if the bidentate phosphine ligand has at least one and preferably each of the aryl groups substituted in the ortho position with an alkoxy group. Such ligands are represented by the above formula wherein each R.sup.1 is 2-alkoxyphenyl. Accordingly, a process for the production of alkali metal di(2-alkoxyphenyl)phosphide would be of advantage.
Production of alkali metal diphenylphosphide by reaction of triphenylphosphine with alkali metal in liquid ammonia is well known. Similar processes to make substituted-phenyl alkali metal phosphides from the corresponding phosphine are satisfactory in some instances and in some instances are not, depending in part on the substituent desired and upon the location on the aromatic ring where the substituent is located. Such a process works well, for example, in the production of alkali metal di(4-methylphenyl)phosphides from the corresponding substituted triphenylphosphines but is not entirely satisfactory for the production of alkali metal di(2-methylphenyl)phosphide.
A production of potassium di(2-methoxyphenyl)phosphide by reaction of potassium and tri(2-methoxyphenyl)phosphine in dioxane at 20.degree. C. is disclosed by Brown et al, Tetrahedron Letters, Vol. 21, pp. 581-584 (1980). The phosphide is formed and subsequently reacted in situ and no conversion of the phosphine to phosphide is specified or was determined.